1. Field of the Invention
This invention pertains generally to respiratory ventilation devices with a constant flow pulmonary modulator and equipped with a manually actuating feature, and more specifically to respiratory ventilation devices with a constant flow pulmonary modulator, as described in U.S. Pat. No. 6,067,984, equipped with a feature to allow the clinician or user to easily manually activate inhalation, thus allowing a user to: 1. cycle the device and initiate inhalation immediately in the event that the device stops providing ventilatory supports and “stalls”; 2. detect if the device is automatically cycling or if the patient is triggering the device; 3. synchronize ventilation with other medical procedures; 4. increase Positive End Expiratory Pressure (PEEP) beyond the intrinsic design value for a given Peak Inspiratory Pressure (PIP) setting; and/or 5. provide an inspiratory hold when desired.
2. Description of the Background Art
A fundamental aspect of providing respiratory care to a patient is the ability to provide ventilatory support to patients requiring respiratory assistance. Ventilatory support is typically provided by clinicians through the use of a manual resuscitator or an automatic ventilatory device.
Manual resuscitators are typically equipped with a self-inflating bag, a set of check valves which control the direction of inhalation and exhalation gases, and a patient interface which is usually either a face mask or a port for connection to and endotracheal tube. Manual resuscitators are usually supplied with a continuous flow of gas containing a known percentage of oxygen. The operator of a manual resuscitator inflates the patient with oxygen enriched air by squeezing the self-inflating bag thus applying pressure and causing gas to flowing into the patient's lungs. Inhalation ends and exhalation begins when the operator stops squeezing the bag, allowing the pressurized gas in the patient's lungs to escape to the ambient environment. Most manual resuscitators are equipped with the means to maintain a small minimum positive pressure on the patient's lungs throughout exhalation commonly called Positive End Expiratory Pressure (PEEP). During exhalation, the self-inflating bag re-inflates and process may be repeated. Manual resuscitators are simple, inexpensive, and are easy to coordinate ventilation with other medical procedures. Unfortunately, manual resuscitators are easy to misuse. A large number of studies have been published which show that irregardless whether the operator of the manual resuscitator is a physician, respiratory therapist or nurse, patients receive volumes of gas per breath (tidal volume) which are too small and respiratory rates which are too quick. This has been shown to create significant adverse effects on patients.
Automatic ventilatory devices (ventilators) were originally developed to deliver a set amount of volume to the patient in a set amount of time which little patient monitoring capability. In the last 25 years different modes, including pressure control, and increased monitoring capabilities have been added, leading to the modern transport ventilators of today. Most ventilators still use volume and time cycled ventilation modes which operate by delivering to the patient pre-set amount of volumes or constant flow for pre-set amounts of time, regardless of the patient's lung compliance. Lung compliance is prone to sudden changes during transport, potentially causing patient airway pressures to increase to the point that they will severely injure the patient. Pressure cycled ventilation and pressure control are newer modes of ventilation used to deliver ventilatory support to the patient and which have a number of distinct advantages over volume and time cycled ventilation modes. Pressure cycled ventilation functions by switching to exhalation from inhalation when a certain pressure is reached, regardless of the volume delivered; thus volumes of gas delivered to the patient vary with variances in lung compliances, preventing the patient from receiving a harmful amount of pressure and insuring appropriate ventilation of the patient.
Modern transport ventilators are battery of pneumatically powered and equipped with numerous ventilation modes, including pressure cycled types of ventilation, various flow control functions, multiple alarm monitoring functions and are also capable of detecting and synchronizing with the patient's breathing efforts. Although current transport ventilators provide consistent, safe and reliable ventilation, they are extremely expensive. Additionally, the disposable accessories that are required to be used with these ventilators can sometimes cost as much or more than a manual resuscitator. To reduce the high capital costs of these devices, some manufacturers have returned to offering simplified time cycled volume ventilators without any of the standard monitoring, control and alarm features of typical ventilators, nor the option of pressure cycled ventilation. These devices are often classified as automatic resuscitators and, in addition to not being as safe, still cost thousands of dollars and require the use of additional disposable or parts which require sterilization before being reused. In today's environment of medical cost containment, hospitals and other medical providers have, for the most part, balked at the cost of transport ventilators and the training of additional personnel it would require.
A Pulmonary Modulator Apparatus (PMA), as described in U.S. Pat. No. 6,067,984 and included herein by reference in its entirety, has been shown to successfully solve the consistency problem of manual resuscitators and the capital expense issues of transport ventilators. Unfortunately a PMA has a number of problems: 1. it can stop cycling due to physiological, mechanical, pneumatic, or environmental changes; 2. it can be hard or impossible for a user to determine if the device is automatically cycling or if the patient is initiating breathing thus increasing the work of breathing for the patient; 3. it is limited to delivering a set level of PEEP that is a constant ratio of PIP; and 4. it has no means of providing an inspiratory hold.
As described in U.S. Pat. No. 6,067,984, a pressure pulmonary modulator apparatus (PMA) comprises a dual area piston (or diaphragm) having a surface area that rests against an interior end of a inlet chamber, thus sealing the inlet chamber during the inhalation phase of the patient. The dual area piston comprises a primary area defined as the area exposed to the patients pulmonary capacity during inspiration when the piston is in the closed position, and a much larger area which comprises the entire area of the piston which is in fluid communication with the patients pulmonary capacity only during discharge or when the piston is in the open position. When the dual area piston is closed, it prevents compressed gas from escaping and causing the lungs to become charged by the incoming compressed gas. During charging (i.e. inspiration), the pressure in the patients lungs increases until the force of the pressure on the primary area of the dual area piston overcomes the restorative force of the piston. Once the dual area piston begins to open, the full area of the piston is exposed to the pressure of the patient's lungs causing the piston to move away from the interior end of the inlet chamber to a fully open position almost immediately. The patient's lung pressure that causes the piston to move into the fully open position is the patient's peak inspiratory pressure (PIP), which is adjustable by controlling the restorative force on the piston. Once the piston opens, it will remain open until the patient's lung pressure drops to a value small enough such that the restorative force overcomes the force of the patient's lung pressure on the full area of the piston. During discharge, the exhaled gases pass by the piston and out of the system through an adjustable flow restrictor (i.e. the rate dial) used to control the rate at which discharge gases are vented into the atmosphere, resulting in the control of discharge duration. The rate dial is essentially a valve, and resistance to exhalation flow is realized by screwing or adjusting the rate dial in our out. Greater resistance to flow results in slower exhalation flows and longer exhalation times. Once the patients lung pressure drops to a value low enough to allow the force of the spring to push the piston closed, the discharge ends and the cycle is repeated.
The patient may spontaneously breathe by triggering the inhalation prior to the end of exhalation. A one-way valve may optionally be provided to increase the ease of the patient's inhalation. Under such circumstances, a new inhalation will start when the patient breathes in, reducing the patient's airway pressure and causing the piston to close and a new inhalation period to start. In addition, the apparatus can be adapted to function as a positive pressure aerosol device by attaching a nebulizer assembly to the inlet chamber of the apparatus. Such a device is useful to those needing the therapeutic effects of aerosol in addition to ventilatory support.
From time to time it may be useful to put the PMA into a “spontaneous mode” in which inspiration starts only after the patient has initiated it by drawing a breath. This mode is achieved by dialing the rate dial to such a position that the restriction to flow for the set flow of gas provided creates an internal pressure great enough that it maintains a greater force on the open piston/diaphragm than the restorative spring force. In such a condition inhalation is initiated by the patient inhaling enough gas that the pressure drops and the restorative force of the spring causes the piston/diaphragm to close.
A PMA can stop cycling, and thus stop providing ventilatory support to a patient, due to physiological, mechanical, pneumatic, or environmental changes. Although this has the benefit of alerting the clinician that the situation is changing, the condition is ultimately highly undesirable because the patient still needs ventilatory support and the only manner that ventilatory support may be provided by existing PMAs is by the clinician determining what change occurred and changing the baseline settings of the PMA to compensate. Determining what change occurred can be time consuming, and if the patient is not being provided ventilatory support, clinicians are rushed and almost always don't have the time. Furthermore, changing the baseline settings of the PMA is often undesirable because it creates a greater degree of uncertainty in a situation that may still be varying and problematic, thus re-stabilizing the patient becomes more difficult. Therefore there is a need for a device with the advantages of a PMA that has the further capability of delivering temporary or alternate ventilatory support regardless of physiological, mechanical, pneumatic, or environmental changes and without changing the baseline settings of the PMA.
Under most circumstances, a PMA is used with a patient who is unconscious and paralyzed due to the administration of medication by the clinician. The sedation of the patient is necessary because it mitigates the risk that the patients will become hypertensive and fight the ventilatory support of the PMA, or that the patient will simply begin to hyper-ventilate. Maintaining the patient in a sedated state can sometimes be problematic because the effects of the medication can subside, or if the medication has just recently been administered, it will take time for the medication to take effect. Much of the time patients are transitioning from one sedated state to another. In the interests of stabilizing the patient, insuring that the work of breathing is appropriate for the patient, and allowing the clinician to address other possible patient conditions, it is important for the clinician to be able to determine if the patient is truly sedated, and that the breathing of the patient is purely caused by the PMA, or if the patient is still semi-active on a respiratory basis and is triggering the device with slight inhalation efforts. Determining which state the patient is in is very difficult to do with the existing PMA design because it is impossible to tell if the patient or the device is causing the cycling of the PMA. Therefore there is a need for a device with the advantages of a PMA that has the additional capability of providing some feedback to the clinician on the sedative state of the patient.
Current PMAs have an intrinsic design PEEP for any set PIP. Since some patients may require additional PEEP beyond what is provided for a set PIP, this is a serious limitation of the PMA. Currently, the PMA may be set to deliver an increased PEEP by adjustment of the rate dial or by increasing flow, but this places the device in a mode that will not cycle unless initiated by the patient which is clearly undesirable the vast majority of the time because it increases the work of breathing of the patient and the patient may simply be unable to make the respiratory effort. The situation can be rectified by addition of an in-line PEEP valve placed between the inlet of the modulator and the patient's airway, but this adds to the cost and clumsiness of the device, and is not practical since additional PEEP is only needed sometimes and as a result clinicians are not likely to keep such devices on hand. Therefore, there is a need for a device with the benefits of existing PMAs that had the additional capability of delivering more PEEP when desired.
Sometimes there is a need for the clinician or user to create an inspiratory hold which is effectively a pause at approximately the peak pressure of inspiration before the initiation of exhalation, or to simply suspend ventilatory support temporarily. An inspiratory hold (clinically also sometimes referred to as sigh breath) can provide important physiological support of certain types of patients. A pause in ventilatory support can provide a needed opportunity for a clinician to perform a needed procedure without the interference of on-going ventilation. Current PMAs do not have this capacity without inducing major clinical inconvenience and disturbance. One method currently employed using existing PMAs is to create a condition in which the entire exhalation path is occluded, potentially leading to damaging pressure levels, and failing to provide a sustained pressure level support. Another is to remove the modulator from patient tee thus eliminating any pressure support of the patient and risking alveolar collapse. Therefore, there is a need for a device with the benefits of existing PMAs that has the additional capacity of delivering an inspiratory hold, or ventilatory pause, in a manner that will limit the pressure level and will not entirely occlude the exhalation path of the patient.
In the pre-hospital environment, many of the Emergency Medical Technicians (EMTs) servicing patients during emergency calls do not have the same sophistication and training as Respiratory Therapists and clinicians in the hospitals. As a result, there is sometimes a reluctance to employ existing PMAs because there is a fear that the EMT may face a situation in which they are not entirely sure what the most appropriate adjustment would be in the event that the PMA stops delivering ventilatory support for mechanical or physiological reasons. Existing PMAs don't have any readily available way to provide these clinicians with a simple back up plan in such event. Therefore, there is a need for a device with the benefits of existing PMAs that has the additional capacity of providing a simple back up plan to clinicians unsure of the changing situation they may be facing.
The present invention has all the benefits of existing PMAs with the added benefit of solving the previously described problems. Specifically the current invention has the advantage that it will: 1. deliver immediate manually triggered ventilatory support regardless of any changes that may have stopped the PMA from automatically cycling (i.e. delivering automatic ventilatory support); 2. provide valuable feedback to the clinician on the sedative/conscious state of the patient; 3. deliver more PEEP than the intrinsic design PEEP of the PMA for the given PIP and flow setting; 4. deliver an inspiratory hold, or ventilatory pause, in a manner that will limit the pressure level and will not entirely occlude the exhalation path of the patient when desired by the clinician; and 5. provides a simple back up plan that still provides ventilatory support to patients for clinicians unsure of the mechanical and physiological situation they are facing.